所…的 (that which…)

Structure (Subject +) 所 + verb + 的 (+ head noun) · 所…的是…

所…的 is the literary relative clause: 所 nominalizes the verb and 的 closes the group, yielding "what… / that which…", with emphasis on the object of the action. 这正是我所需要的 "this is exactly what I need" matches the relative with bare 的 (我需要的), but 所 makes it more emphatic and formal. It allows the variant 所…的是… for topicalizing: 我所担心的是时间不够 "what worries me is that there isn't enough time". Compared with plain …的 (HSK 1–2), adding 所 raises the register and highlights the object.

Examples

这zhè正zhèng是shì我wǒ所suǒ需xū要yào的de。
This is exactly what I need.
我wǒ所suǒ担dān心xīn的de是shì时shí间jiān不bù够gòu。
What worries me is that there isn't enough time.
他tā所suǒ说shuō的de话huà与yǔ事shì实shí不bù符fú。
What he said does not square with the facts.
我wǒ们men所suǒ追zhuī求qiú的de是shì公gōng平píng与yǔ正zhèng义yì。
What we pursue is fairness and justice.

Levels are indicative: they follow the standard Chinese Grammar Wiki (AllSet Learning) progression, not an official HSK 3.0 mapping. We never assign levels by eye.

This point and the other 370, with audio on every example, inside Wanyu.